1. Field of the Invention
The present invention relates to an organic light emitting device (OLED) and a method of fabricating the same and, more particularly, to an OLED and a method of fabricating the same, which includes a pixel electrode with a triple-layered structure, having a reflective layer made of Ag interposed, therein.
2. Description of the Related Art
In general, an OLED is an emissive display device electrically exciting a fluorescent organic compound to emit light. The OLED is classified into a passive matrix OLED and an active matrix OLED depending on the type of driving N×M pixels. The active matrix OLED (AMOLED) is used with large screen displays and has high resolution. Further, the AMOLED consumes less power than the passive matrix OLED (PMOLED).
The OLED is further classified into a top emission OLED, a bottom emission OLED, and a both sides emission OLED depending on the direction of light emitted from an organic compound. The both sides emission OLED simultaneously performs top and bottom emission. The top emission OLED, i.e., a device for emitting light in an opposite direction of a substrate, at which unit pixels are disposed, has a higher aperture ratio than that of the bottom emission OLED.
Demand for the both sides emission OLED including a main display window of the top emission OLED and an auxiliary display window of the bottom emission OLED is increasing. The both sides emission OLED is commonly used in mobile phones, which includes an auxiliary display window at an outer part and a main display window at an inner part. The auxiliary display window uses less power than the main display window to continuously maintain an “on” state when the mobile phone is in a standby state, thereby displaying, for example, a signal receiving state, a battery state of charge, current time, etc., of the mobile phone.
FIG. 1A is a cross-sectional view of a conventional OLED. First, a buffer layer 110 of a predetermined thickness is formed on a substrate 100, and then a thin film transistor including a polysilicon pattern 122, a gate electrode 132, and source and drain electrodes 150 and 152 is formed. Source and drain regions 120, at which impurities are ion implanted, are provided at both sides of the polysilicon pattern 122, and a gate insulating layer 130 is disposed on an entire surface of the resultant structure.
A passivation layer 160 of a predetermined thickness is then formed on the entire surface of the resultant structure, and the passivation layer 160 is etched by photolithography and etching processes to form a first via-contact hole (not shown) to expose one of the source and drain electrodes 150 and 152, for example, the drain electrode 152. The passivation layer 160 is an organic insulating layer formed of silicon nitride, silicon oxide, or a stacked structure thereof.
A first insulating layer 170 is then formed on the entire surface of the resultant structure. The first insulating layer 170 may be formed of a material selected from a group consisting of polyimide, benzocyclobutene-based resin, spin on glass (SOG), acrylate, and the like, which is formed to planarized a pixel region.
The first insulating layer 170 is etched by the photolithography and etching processes to form a second via-contact hole (not shown) to expose the first via-contact hole.
A stacked structure of a reflective layer (not shown) and a thin layer for a pixel electrode (not shown) is then formed on the entire surface of the resultant structure. The reflective layer is formed of a highly reflective metal, such as Al, Mo, Ti, Au, Ag, Pd, or an alloy thereof. When the reflective layer is formed according to the above described process, the top emission OLED is formed, and when the reflective layer is formed according to the process described below, the bottom emission OLED is formed.
The bottom emission OLED is formed with a thin layer for the pixel electrode having a thickness of approximately 10 Å to −300 Å, using a transparent metal material, such as ITO (indium tin oxide).
The stacked structure is etched by the photolithography and etching processes to form a pixel electrode 182 and a reflective layer pattern 180a. 
A second insulating layer pattern 190 for defining an emission region is then formed on the entire surface of the resultant structure. The second insulating layer pattern 190 may be formed of one material selected from a group consisting of polyimide, benzocyclobutene-based resin, phenol resin, acrylate, and the like.
An emission layer 192 is formed in the pixel region defined by the second insulating layer pattern 190 using a low molecule deposition method or a laser induced thermal imaging method. An opposite electrode (not shown) is formed to complete the OLED. For example, when forming the top emission OLED, the opposite electrode is formed of a transparent electrode or a transparent metal electrode, and when forming the bottom emission OLED, the opposite electrode is formed of a metal electrode or a reflective electrode including a reflective layer.
Thus, when the top emission OLED is formed in a stack-like structure of the reflective layer pattern 180a and the pixel electrode 182, the reflective layer pattern 180a and the pixel electrode 182 are simultaneously exposed to an electrolyte solution used in the photolithography and etching processes, resulting in a galvanic phenomenon when a material having large electromotive force of the stacked structure is corroded, thereby damaging the pixel electrode. As a result, optical characteristics, such as brightness, are deteriorated.
FIG. 1B is a cross-sectional view of an OLED formed by another conventional process. Referring to FIG. 1B, to solve the problems, a reflective layer pattern 180b is formed having an island structure. Thus, the reflective layer pattern 180b and the pixel electrode 182 may not be simultaneously exposed to the electrolyte solution used in the photolithography and etching processes.
As described above, when the reflective layer pattern is formed of Al, the reflective layer pattern and the pixel electrode should be separately patterned. In addition, since the top emission OLED uses a resonance effect of light, it is important to allow color coordinates to be readily adjusted by forming the pixel electrode as thin as possible. However, when a thin pixel electrode is formed a short circuit is likely to be generated at a step portion of the via-contact hole.